Electronic cooling by wick boiling and evaporation



Dec. 4, 1962 J. T. FISHER ETAL 3,066,499

ELECTRONIC COOLING BY- WICK BOILING AND EVAPORATION Filed Jan. 2, 1959 5Sheets-Sheet 1 fNI ENTOES Dec. 4, 1962 J. T. FISHER ETAL 3,066,499

' ELECTRONIC COOLING BY WICK BOIL'ING AND EVAPORATION Filed Jan. 2, 19595 Sheets-Sheet 2 fie. 2.

Doodle A Pah/e/I Dec. 4, 1962 J. T. FISHER ETAL 3,066,499

ELECTRONIC COOLING BY WICK BOILING AND EVAPORATION Filed Jan. 2, 1959 5Sheets-Sheet 3 [NI/ENTOES Dec. 4, 1962 J. T. FISHER ETAL ELECTRONICCOOLING BY WICK BOILING AND EVAPORATION 5 Sheets-Sheet 4 Filed Jan. 2,1959 Myrna/e5 00/; a/a 4. Per /er. Jam 7' F/J- Dec. 4, 1962 J. T. FISHERETAL 3,066,499

ELECTRONIC COOLING BY WICK BOILING AND EVAPORATION Filed Jan. 2, 1959 5Sheets-Sheet 5 United States Patent Ofilice 3,956,499 Patented Dec. 4,1962 3,066,499 ELEQTRONIC COOLING BY WIQK BOELING AND EVAPORATION JohnT. Fisher and Donald A. Potter, Indianapolis, Ind, assignors to Stewartl/Varner Corporation, Chicago, Ill., a corporation of Virginia FiledJan. 2, 1955 Ser. No. 784,675 4 Claims. (Cl. 62-316) This inventionrelates to cooling of electronic equipment by wick boiling andevaporation and more particularly to a wick cooled electrical component.

In electronic equipment of the prior art in which liquid is used forcooling employing the submerged or pool boiling principal, it isnecessary to fix the equipment in a stationary position in order to keepthe liquid in its proper place, or as an alternative complicated meansmust be provided to contain the liquid and at the same time enable theresulting vapor formed from any boiling coolant to escape to theatmosphere. Some electronic units employ complex vent or check valveswhich permit one side or the top of the unit to be open to atmosphere,while the other sides and bottom remain closed to prevent loss of theliquid coolant. This type of exchanger requires means for closing one ormore of the valves should the exchanger be turned on the side or itstop, and means for opening one or more of the valves to permit escape ofvapor to the atmosphere. Other prior art electronic units employ areservoir sufiiciently large so that a vent pipe extending approximatelyinto the middle of this reservoir is always above the level of liquidregardless of the attitude of the exchanger. Obviously, if the exchangeris inverted, the liquid coolant is at best in contact with only aportion of the heat exchange surfaces. This mode of operation reducesthe cooling of the liquid exchanger during those periods in which all orpart of the liquid is not in contact with the heat ex change surfaces,as well as being complex in structure.

The prior art electronic equipment employing cooling of this type coolsthe entire unit or a major portion of the unit, because it has areservoir for containing the water of suificient size to hold therequired quantity of liquid. This reservoir, therefore, extends over alarge portion of the electronic unit. This arrangement makes itdifiicult if not impossible to selectively cool one or more of the unitswhich require cooling while the balance do not. Additionally, electronicunits which employ submerged boiling or evaporation and which have areservoir to contain the liquid coolant must employ a leakproofreservoir to prevent spillage to the outside or to the electronicchassis.

An object of the invention is to provide equipment having a plate memberhaving wetted wick material on one side and an electrical component onthe other side thereof.

Another object of this invention as applied to electronic equipments isto retain the coolant liquid against the hot portions of an electronicchassis with the electronic unit in any attitude through the use of asimple construction employing a wick and not necessarily requiringvalves or bafi les.

Another object is to provide in an electronic chassis a simple andreliable wick means for distributing to the hot surfaces a liquidcoolant from a storage reservoir. The liquid is carried from thisstorage reservoir and distributed to the hot surfaces by wick action.

Another object is to reduce the Weight and size of an electronic chassisin which cooling is necessary and at the same time maintain a high heatexchange efficiency by using a wick to bring the least amount of liquidin contact with the heat exchange surface required to establish auniform Wetting thereof.

Another object is to provide means for placing a liquid coolant directlyagainst the hot surface of the electronic component to be cooled ratherthan employing an inter mediate liquid type wall which is necessary inprior art devices to prevent spillage of the liquid coolant.

A preferred embodiment of the electronic cooling ap' paratus of thisinvention employs a wall member with wetterl wick material on one sideand electrical and/or electronic components on the other side thereof.The wall member comprises a chassis having recesses for the componentsand other electrical components not requiring so heavy cooling as thosein the recesses may be mounted on the component side of the chassis.Those units which are not enclosed within the recesses in the chassismay be protected by a cover. Also, the electrical or electronic unitwhich requires cooling may be surrounded by a sheath having wetted wickmaterial therearound.

The wick material may communicate with a source of liquid coolant andthe coolant is carried to the hot surface of the unit by wick action.The liquid coolant is elevated to a boiling temperature upon contactwith exchange surfaces, and the resulting vapor is permitted to escapeto the atmosphere. The wick material retains the liquid coolantindependently of the attitude of the electronic equipment and withoutthe use of valves or other arrangements. Preferably a vented casingencloses the wick material and forced draft cooling of the wick materialmay be employed.

A second preferred application of the electronic cooling principles ofthis invention employs the placement of all of the parts of theelectronic unit which must be cooled on top of a chassis and surroundingcomponents with the wick material. A cover of the electronic chassis inthis serves also as the container for the wick ma terial. Thisarrangement protects the entire equipment from extreme temperaturesgenerated outside of the etlectronic unit such as the high ambienttemperatures encountered in high speed aircraft.

In a third preferred application of the electronic cooling principles ofthis invention, those parts of the electronic unit which must be cooledare mounted on top of the chassis, and wick material is enclosed in apressure tight container fitting down over the protruding electroniccomponents in the manner of a glove being pulled over a finger. Thepressure tight enclosure may have one or more projecting portionsprotrudnig down into the electronic chassis to cool components below thechassis. There also may be provided a pressure regulating vent valve toregulate the pressure at which the liquid coolant boils, thus regulatingits temperature.

Another application of the electronic cooling features of this inventionutilizes wick material enclosing electrical units to be cooled andretained in a foraminous member. Cooling air may be circulated bysuitable means over the foraminous member causing evaporation of theliquid and consequent cooling.

In order that all of the structural features for attaining the objectsof this invention may be readily understood, detailed references areherein made to the drawings, wherein;

FIG. 1 is a perspective view, partly in section, of a device forming oneembodiment of the invention and having one of the electronic componentssurrounded by a wick to show the principle of this cooling method;

FIG. 2 is an enlarged, vertical sectional view of the device of FIG. 1and taken along line 2 2 of FIG. 1;

FZG.,3 is a vertical sectional view of a device forming anotherembodiment of the invention;

FIG. 4 is an enlarged fragmentary vertical sectional View of amodification of the device of FIG. 1;

FIGS. 5, 6 and 7 are perspective and vertical views of ci a deviceconstituting a further embodiment of the invention; and

F165. 8 and 9 are vertical sectional views of devices forming alternateembodiments of the invention.

Referring in detail to the drawings, an electronic device 1t (FlGS. 1and 2) has an outer shell 11 enclosing internal electrical and/orelectronic components 12 of the device. For convenience of design,certain of the electronic components are enclosed within the shell 11and a chassis 131, and other components 14 are placed on top of andprotrude from the chassis. Those electronic components which are placedon top of the chassis are enclosed with cover l which has suitableopenings 16 to allow air to circulate for ventilation and cooling.Electronic component 17, which requires cooling is enclosed with anannular band of v/ick material Whic is held in place by annular pan orcontainer 19, around the surface of the electronic component, which issheathed extcriorly by a waterproof sheath. Container 19 has a snugfitting upturned lip 26 which makes a reasonably tight contact with theelectronic component 1'7. The cover is held to the electronic chassis byknown socket means.

The wick material '13 is advantageously suited for use in a system inwhich all of the liquid necessary for cooling can be contained withinthe amount of wick material placed in the container, for example,aircraft applications requiring but a few minutes of cooling. Themaximum time is obtained by filling the spaces occupied by the wickmaterial 18 with liquid coolant. This may be accomplished by a suitablebulb type filler 2.1, such as used for putting Water in automobilebatteries or with a suitable tube and funnel 22, which may be placedoutside the electronic unit. As boiling or evaporation takes place tocool the electronic component, the amount of liquid diminishes, with theresulting vapor being released through the openings 16 in the cover.This action takes place because of contact of the Wick material with thesheathed electronic component 17 on its outer surface. The contactingportion of the wick 13 then contains less moisture than the balance ofthe material, and the moisture that remains in the balance of thematerial is carried to the hot surface by the small capillary openingsin the wick material to supply these surfaces with a constant amount ofliquid to keep them wet. With this occurrence, the wick material willcontinue to draw the liquid to this hot surface by capillary attractionthrough its entire length, thereby keeping the hot surface supplied withliquid. At the same time, because the wick material 18 is porous, itpermits the vapor to escape from all parts of this hot surface andtravel upward to the openings in the cover 15. If the unit is turned onits side or inverted, the liquid will still be retained by the wickmaterial and vapor will still travel to the openings 16 as the boilingaction continues to take place.

if it is not convenient because of space or other limitations to providesufficient wick material to contain a large enough quantity of liquid tocool for the time desired, then a separate reservoir 25 (FIG. 3)containing an additional supply of liquid 26 may be provided. Thisreservoir is connected in the same manner with tube 22A, as the fillerfunnel 22 is connected to the container holding the wick material. Thereservoir is equipped with a suitable filler cap 27. The wick material18 in the unit of FIG. 1 is placed only around the sides of theelectronic component 17 to be cooled, leaving the top open andaccessible for wires or terminal connections 28 to the component.

Referring to FIG. 3, an additional component 17A may also be cooled aswell as component 17. This can be accomplished by enclosing component17A with wick material 13A, which is held in place by container 19A, andconnected with a piece of tubing 223, which is an extension of thetubing 22A supplying Wick 18. The liquid 25 in reservoir 25 now suppliesthe two electronic components and may be made in any size to accommodatethe required amount of coolant. Reservoir 25 is suitably located outsidethe cover 1.: so that the level of liquid will not be higher than thelevels of the wick material 18 and 13A to prevent overflow of thecoolant during the filling operation of the reservoir. Since time isinvolved for the liquid to travel from the bottom of the container 19and MA in the wick material to the top (this time for liquid to travelthrough the Wick is known is the wicking rate), the electronic unit maybe turned on its side, tilted or turned upside down a position in whichthe liquid level in the reservoir would be higher than the upper mostportion of the Wicks. There is a time, therefore, before the liquid willrun out of the wick material because if its being saturated during whichthe unit which may be in an aircraft may be on its side or invertedbecause of a maneuver of the aircraft. If it is desired to extend thistime because of the duration of the maneuver, than additional wickmaterial may be placed in tubes 22A and 223 to slow up the rate at whichliquid will travel to the wicks.

in the electronic unit shown in FIG. 4, sheathed electronic component 14mounted on chassis 115 is cooled by evaporative Wick unit 28 Whichcomprises an inner flanged metal tube or socket cup 29 fittingly snuglyover the sheath of component 14 and held securely thereon by friction.The tube 29 is suitably sealed by brazing of flanges of chamber 30 andwick material 31 of fiber glass or other suitable wicking substantiallyfills the con tainer formed by the elements 29 and 30. The chamber 30has top vent tube 33 closed by a perforated cap 34. The chamber also hastop filling tube 35 closed by cap 36 for supplying liquid coolant to thechamber. Flanged chassis 13 is secured by screws to the cover to form aclosed compartment and flanges of the chassis and cover 15 are securedtogether by screws 37.

The electronic unit 40 shown in FIGS. 5, 6 and 7 has cover 41 enclosingthose components 12 which need not be cooled externally. Components 42,42A and 42B are fixed to the top of the chassis. Components 45 such astransistors, and the like, whose temperature may be critical are mountedon a cold plate 46, and are cooled by thermal conduction to the plate 46which has outer surface 43 in contact with Wick material 48.

The cold plate 46 may be mounted on top of the chassis as 46 in achamber 49 and may be an integral part of the chassis 51. The cold plateis shown as mounted in face to face contact with cover 50 so that thecomponents mounted and connected make a component assembly with thecover, and the cover is embedded in the Wick material, and theseelements may be considered a component for cooling purposes.

The electronic unit 49 may consist of any combination of these describedcomponents or component assemblies.

The chassis is enclosed by bottom cover 52 and top cover 53. The wickmaterial 48 is contained Within the cover 53 and is supported on asuitable platform or pan 54. The mass of wick material 48 isproportionately large in volume and thus Would have the potential tocool a large number of electronic components. Coolant liquid is pouredinto combined filling and vent opening 56 in the cover 53 until thedesired quantity is contained in the wick material. The capillaryopenings in wick material 48 causes the coolant liquid to spread evenlythroughout the mass of this wick material. When the electronic equipmentis operated, the individual components to be cooled will dissipate theirheat on the outer surface of the components or the plates 46 and 47.Inasmuch as the Wick is in contact with these surfaces, the coolantliquid is boiled or evaporated from these surfaces. The porous wickenables the vapor to escape to the space 57 Where it proceeds outthrough the opening 56 to the atmosphere.

FIG. 5 is a view showing details of pan 54. The pan liquid tight troughin the immediate vicinity of component 42 located under or close to theopening 56 into which the coolant liquid is admitted. As the coolantliquid is poured into this opening, it will travel with an equal speedin all directions and will reach the opening 64 in drain tube 62 at thesame time it would reach a point in the Wick material equally distantfrom the drain opening. At this point, a mass of wick material ofdimensions equal to the distance from tube opening 64 to the top will besaturated with this liquid. If at this instant, more liquid is pouredinto the wick and can travel further throughout its mass, then theexcess will run out of tube 62 in the form of drops. If at this point,the entrance of the coolant liquid ceases, then the coolant willdistribute to the balance of the mass of the wick material through itscapillary openings until it is evenly distributed. At this point, thewick material immediately above the tube opening 64 will be onlypartially saturated and thus can hold more of the coolant. Now anadditional quantity of coolant can be introduced into the mass ofwicking until the excess again runs out of overflow tube 62. In thisfashion, the entire mass of the wick material can be brought close tothe point of saturation with the coolant liquid. The rest of support orpan 54 to the left of the component 42 as viewed in the drawings, thusdoes not need to be liquid tight since excess liquid will not leave thewick material unless it is saturated. Thus additional openings, such as65 need not have the water tight lip formed on them if it is not desiredto do so. In this fashion the mass of wick can be made to hold itsmaximum quantity of liquid without having any of it spill onto the topof the electronic chassis or ouside of the cover. Because of thisfeature, both the cover 53 and the platform -4 need not be liquid tightexcept in the area previously described. The electronic unit 40 may beturned on any one of its sides or upside down while in this saturatedcondition and the boiling action against the hot surface 43 willcontinue to take place the vapors will escape to space 57 and outopening 56 regardless of attitude of the unit.

Referring now to FIG. 8, electronic unit 70 contains electroniccomponents 71 enclosed by downwardly facing recesses 72 in partition 73.Components 74 not liberating sufficient heat to require external coolingare enclosed in cover 75. Components 71, 71A, and 71B are mounted on topof the chassis or partition to receive cooling. The components 71B maybe cold plate assemblies. The partition 73 forms a pressure tight coverarranged with the suitable sleeve type openings to enclose theelectronic components. The wall of the openings 72 fit over thecomponets snugly so that they make contact or a space may be leftbetween the sleeve and the component and filled with a finger contacttype material and/or aluminum or other metal wool 76 to conduct the heatfrom the electronic component to the sleeve 72. The pressure tight cover73 is secured to the chassis through suitable fasteners 77. Wickmaterial 78 is suitably arranged in layers or other form insidecontainer 79. Filling tube 80 selectively closed by pressure tight cap81 is provided for filling this container with liquid coolant. Liquidcoolant is poured through this opening until the wick material issaturated or the desired quantity of liquid has been admitted. Thecoolant will diffuse evenly throughout the mass of wick material,through the capillary openings in the wick. Vent tube 82 is filled withforaminous material 83 such as wicking, for example.

The partition 73 includes a hollow projection or finger 86 fittingsnugly into sleeve 87 of coil 88 in the lower chamber. The wetted wickmaterial 78 fills the finger 86 to very effectively cool the coil 88 byevaporation.

When the electronic equipment is operated, the heat is dissipated fromcomponents 71 through their outer walls to the conducting material, 76to the sleeves 72 of the container. The opposite surfaces of thesesleeves are in contact with the liquid saturated wick and cause theliquid coolant to boil or evaporate. The vapors thus formed will findtheir way through the porous wick material to space 89 provided betweenthe top of the wick and the pressure tight case 79. The vapors will thenfind their way to the outlet 82 and will be discharged overboard. If itis desired to regulate the boiling temperature of the coolant liquid aknown pressure valve (not shown) may be added to the vent outlet. Thiswould be the case where it is desired to boil water at say 14.7 psi.absolute (sea level pressure) and then upon reaching an altitude wherethe ambient pressure is considerably lower maintain the same boilingpressure or temperature by virtue of having the pressure vent valve setto release the vapors at the desired pressure. The control valve may beset for any pressure and thus control the coolant liquid at anytemperature level.

The vapor or steam, if water is used as a coolant, will form on theouter faces of the sleeves 72 between these faces and the wick material.Normally the vapor will rise along these faces until it must enter thewick material and then will find its way through the porous portions ofthe wick to space 89. The passage of this vapor through the wickmaterial will cause a pressure drop in the vapor. In other words, thepressure at space 89 must be lower than the pressure at source of thevapors in order to have this vapor escape. This pressure may be added tothat obtained by the control valve to regulate the boiling temperature.However, if this pressure drop is undesirable, then passages 90 oropenings on top of the sleeves may be provided in wick material byforarninous sleeves 91 of screening or the like. The vapor thus isallowed to travel along the outer faces of sleeves 72 where the pressuredrop is negligible into the opening 90, and thus to the space 89 on topof the wick with no appreciable pressure drop. This may be desirablewhere it is necessary to have the minimum boiling temperature(pressure).

It may be desirable to mount components 71C as a cold plate assembly onthe underside of the partition 73. This may be done on a portion or wallof this surface. Thus it is possible to cool selectively either certainportions or all of the entire electronic equipment. This would bedesirable in the event that outside ambient temperatures were such thatthe chassis components required cooling at these high ambient conditionswhere they might not at more normal ground level conditions.

While the unit 78 is described as an open system in which the vaporsfrom the liquid coolant are-vented to atmosphere, it will operateequally well as a closed system. A tube or pipe would be connected tothe outlet 82 to carry the vapor to a compressor then a condenser to beliquified by a conventional refrigeration cycle. The coolant liquidwould then enter the pressure tight case 73, through a control valve andpiping to tube 80.

Referring to FIG. 9, electronic unit 95 has a chassis 96 and a bottomcover 97 enclosing electronic components 98 inside. One or more sheathedcomponents 99 requiring cooling are placed on top of the chassis andenclosed by and in contact with sleeves ltltl of wick material, which iscontained in an open sleeve 181 or screen wire or equivalent andsupported by flanged annular discs 102. Component 183 is shown mountedon cold plate 104 with a mass 105 of wicking retained by screen 106 andframe 107 on top of the chassis directly above the cold plate 104. Theseunits are arranged to be enclosed by cover 111 which has opening 112 toadmit forced draft cooling air. Coolant liquid may be placed in the wickmaterial by any of the methods previously described, vent openings 113being provided. Cooling air may be induced to flow over the wickmaterial by natural draft or by induced draft circulation. The coolantliquid evaporating into this air stream will'lowcr the coolanttemperature to that close-to the wet bulb temperature of the enteringcoolant air. Thus it is possible to cool the electronic component belowthe boiling point of the coolant at that particular ambient pressure byevaporation of the coolant into the ambient air. This is important forsuch items as transistors many of which must be kept below 175 to 200 F.This evaporation in turn will lower the temperature of the air as wellas cool components 99 and 103, and the cooler air may be then used toprovide an additional amount of cooling for the balance of thecomponents over which it will circulate.

The above units very efifectively cool the electronic components, andare simple, light, rugged and inexpensive in construction.

'It should be understood that the above described examples are merelyillustrative of the principles of this invention, and that numerousmodifications may be devised by those skilled in the art withoutdeparting from the scope of the invention.

What is claimed as new is:

1. A selectively cooled electrical component assembly comprising anenclosure assembly forming a plurality of chambers, means mounting onecomponent in a first one of the chambers, heat conducting platestructure mounting a group of components in a second one of thechambers, means mounting components requiring little or no cooling in athird one of the chambers, the enclosure structure forming an additionalchamber having common wall heat transfer structure withthe otherchambers, and wetted wick material substantially filling the additionalchamber and substantially surrounding the common wall portions of theadditional chamber for selective evaporative cooling of the electricalcomponents.

2. A selectively cooled electrical component assembly comprising anenclosure assembly forming a plurality of chambers, means mounting onecomponent in a first one of the chambers, heat conducting platestructure mounting a group of components in a second one of thechambers, means mounting components requiring little or no cooling in athird one of the chambers, the enclosure structure forminga-n additionalchamber having a common wall heat transfer structure with the otherchambers varying in area generally in accordance with the relativecooling required by .the components in the respective chambers, andwetted wick material substantially filling the additional chamber andengaging the common wall structure for selective evaporative cooling ofthe electrical components.

3. The combination of claim 2 together with means forming unrestrictedvapor conducting passages in the Wick material extending from positionsadjacent the upper ends of the first and second chambers to the uppersurface of the wick material.

4. The combination of claim 3 together with metal wool packed betweenthe one component and the adjacent portion of the common wall'structurefor rapid conduction of heat from the one component.

References Cited in the file of this patent UNITED STATES PATENTS178,761 Gimmy June 13, 1876 748,296 Miller Dec. 29, 1903 1,063,312Amsbary June 3, 1913 1,155,701 .Bliss Oct. 5, 1915 1,231,088 StafiordJune 26, 1917 2,030,155 Roberts Feb. 11, 1936 2,643,282 Greene June 23,1953 2,670,941 Feinberg Mar. 2, 1954 2,715,518 Bickler Aug. 16, 19552,799,793 De Cain July 16, 1957 2,867,991 .Makowski Jan. 13, 19592,901,893 .Saltzman Sept. 1, 1959 2,906,103 S-altzman Sept. 29, 1959FOREIGN PATENTS 481,770 Great'Britain Mar. 17, 1938

